CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (21,975)	$ 512,218	$ 145,013
Other comprehensive income (loss):
Foreign currency translation adjustments, net of deferred income taxes of $1,284, 2,507 and $(2,167) in 2020, 2019 and 2018, respectively	20,760	15,498	(50,743)
Net gain (loss) on cash flow hedging instruments, net of deferred income taxes of $79, $1,438 and $(1,130) in 2020, 2019 and 2018, respectively	(2,123)	(5,106)	2,101
Pension liability adjustments, net of deferred income taxes of $384, $(3,244) and $854 in 2020, 2019 and 2018, respectively	(73,938)	(10,478)	27,185
Unrealized gain (loss) on marketable securities, net of deferred income taxes of $2, $(11) and $16 in 2020, 2019 and 2018, respectively	(6)	28	(48)
Total OCI	(55,307)	(58)	(21,505)
Total comprehensive income (loss)	(77,282)	512,160	123,508
Less: Comprehensive income attributable to noncontrolling interests	(7,178)	(7,327)	(5,454)
Comprehensive income (loss) attributable to Harsco Corporation	$ (84,460)	$ 504,833	$ 118,054